1. Technical Field
The present invention relates to methods for repairing spinal disorders. More particularly, the present invention relates to a method of repairing spinal disorders, especially those requiring spinal fusion, using a biocompatible osteogenic band which induces new bone growth formation at the site of implantation.
2. Description of the Related Art
The vertebral column (spine) is a biomechanical structure composed of a series of joints known as motion segment units. Each motion segment unit includes two adjacent vertebrae and their facet capsules, the intervertebral disc, and connecting ligament tissue. The spine is divided into four major regions which include the cervical, thoracic, lumbar and sacral regions and functions to protect the spinal cord and nerve roots, and provide support to the body. The intervertebral disc is located between the two endplates of adjacent vertebrae and is composed of the nucleus pulposus (a gel-like ball located at the center of the disc) and annulus fibrous (collagen fibers surrounding the nucleus pulposus). The intervertebral disc stabilizes the spine, and provides the spine with resiliency and the ability to withstand compression, rotation and bending strain. The facet capsules are bony elements which aid in the support of compressive loads and resist torsional motion. Ligaments connected to the spine support loads in tension and help provide spinal stability by limiting excessive range of motion and absorbing energy applied due to trauma.
Various types of spinal disorders are known and include kyphosis (backward curvature of the spine), spondylolysis, spondylolisthesis (forward displacement of a lumbar vertebrae), scoliosis (abnormal curvature of the spine) and disorders involving ruptured, slipped, damaged and diseased discs, damaged vertebrae, and the like. Patients suffering from the aforementioned disorders typically experience severe pain, numbness, decreased mobility, muscle weakness and nerve damage.
Spinal fusion is frequently used as a treatment for such disorders and is achieved by formation of a bony bridge between adjacent motion segments eliminating the intervertebral joint. Spinal fusion can be accomplished within the disc space, anteriorly between adjacent vertebral bodies and/or posteriorly between consecutive processes, e.g., transverse processes, laminae or other posterior elements of the vertebrae.
One frequently used spinal fusion technique involves removal of the intervertebral disc and insertion of an anterior supporting structure, e.g., bone grafts, bone substitutes, plugs, bone dowels, cages, and the like, into the intervertebral disc space to prevent collapse of the disc space and promote fusion of the adjacent vertebrae. To ensure proper growth and fusion between the affected adjacent vertebrae, the posterior side of the spine is frequently stabilized by utilizing a rigid metallic implant, e.g., a plate, rod, wire or strip, which spans the adjacent vertebrae to re-create a load distribution similar to that of the intact spine. These metallic implants are commonly referred to throughout the relevant scientific and medical literature as “tension bands.”
The use of such metallic implants to stabilize the spine and facilitate fusion presents several disadvantages. One disadvantage encountered utilizing such metallic implants is that once fusion occurs the metallic implant becomes superfluous and remains as a permanent foreign fixture. As the metallic implant loosens enough to allow relative motion, particulates are generated as wear debris. This wear debris then has the potential to cause a foreign body response. Metallic implants are also subject to fatigue failure due to repeated cyclic loading. An implant that is remodeled, and then repaired as it later becomes damaged, will not fail due to fatigue. Another disadvantage is that the implanted metallic implant itself possesses ferromagnetic properties and thus prevents the use of post-operative plain film X-rays, MRI or CT scan imaging due to scattering of the image. Yet another disadvantage is that when such metallic implants are placed over bone tissue, any tension load placed on the spine is transmitted to the implant rather than the bone tissue, thereby “stress shielding” the bone. Over a period of time, bone tissue that is shielded from tension loads is removed by the body thereby weakening the structure of the bone. Accordingly, removal of the implant by a second operation may be required to prevent loss of bone tissue caused by stress shielding.
In view of the aforementioned limitations posed by using rigid metallic implants to stabilize the spine and facilitate fusion, there is a need to provide a method of treating spinal disorders that will provide for the fusion of bone at the implant site, thereby providing a graft that will not fail mechanically or cause rejection in the patient, and will not require removal in a subsequent operation.
Therefore, it is an object of the present invention to provide a method of stabilizing the spine which overcomes the limitations of rigid metallic implants.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that is non-antigenic and will not be rejected by the host.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that is biocompatible and will not require removal in a subsequent operation.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that is osteogenic and that adequately supports tension loads.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that will avoid stress shielding.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that supports fusion between adjacent vertebrae.
It is a further object of the present invention to provide a method of stabilizing the spine with a device which can be utilized in conjunction with an anterior supporting structure.
Other objects of the invention will be apparent to those skilled in the art in view of the above objects and the foregoing specification.